The present invention relates to a machining tool and, more particularly, to a precision table for use in a machine tool such as a multi-dimensional measuring machine, a surface grinder, or the like, in which a precision table is mounted for selective movement in two directions.
A conventional machine tool table arrangement movable in two directions or dimensions is illustrated in FIG. 1 and includes a so-called V-flat slide bearing. A bed 101, in general, made of castings, is provided with an upper surface in which is disposed a groove 102 having a V-shaped cross-sectional configuration with a flat portion 103 being provided at a position spaced from the V-shaped groove 102. Both the V-shaped groove 102 and the flat portion 103 are machined or worked by scraping with a lubricating oil being stored in a minute concave portion which has been scraped. A saddle 104 is provided which includes along a lower edge thereof a V-shaped projecting portion 105 and a flat portion 106 which are adapted to engage the V-shaped groove 102 and flat portion 103 of the bed 101.
The disposition or positioning of the saddle 104 is regulated by the V-shaped groove 102 of the bed 101 so as to permit the saddle 104 to be displaced linearly. A further V-shaped groove 107 is formed on an upper portion of the saddle 104 with a flat portion 108 being provided on the saddle 104 at a position spaced from the V-shaped groove. The groove 107 is similar to the V-shaped groove 102 as are the flat portions 103 and 108. The V-shaped groove 102 and flat portions 103 provided on the upper surface of the bed 101 extend in a direction perpendicular to the V-shaped groove 107 and flat portion 108 provided on the saddle 104.
A workpiece receiving table 109 is provided having arranged on a lower portion thereof a V-shaped projection 110 and a flat portion 111 which correspond to the V-shaped groove 107 and flat portion 108 of the saddle 104, respectively. The table 109 is arranged so as to be displaceable in the V-shaped groove 107 of the saddle 104 so as to execute linear motion.
In the conventional construction of FIG. 1, the table 109 and saddle 104 can be moved in independent directions and, as a result thereof, the table 109 can be moved in two directions, that is, can execute a planar motion. This type of two-dimensional table is used in a wide variety of machine tools such as, for example, milling machines, surface grinders, or the like, as well as measuring instruments such as a three-dimensional measuring apparatus, photo-repeater or the like, as well as on a precision instrument.
While the proposed conventional table may be easily constructed, one disadvantage in such construction resides in the fact that the table is moved through a slide bearing in which the bearing portions are brought into metal contact with each other.
A further disadvantage of the proposed conventional table resides in the fact that the corresponding bearing portions, that is, the V-shaped groove, V-shaped projection and flat portions, respectively, are in engagement when stopped so that static friction is considerable such that a relatively large application of power is necessary to move the table or saddle from a stopped condition.
Another disadvantage of the conventional table resides in the fact that once the table and saddle are moved, the power necessary to move them can be reduced since the table and saddle are lifted by the lubricating oil; however, the power required to move the table or the saddle varies greatly. Thus, in the proposed table, not only is a smooth movement of the table difficult, but also a precise positioning of the table may not easily be obtained.
Yet another disadvantage of the conventional machine table resides in the fact that the lifting in the table which arises when moving may cause an error in upward or downward direction of the table. The lifting quantity is a large value of 2-5 .mu.m. Consequently, in the conventional table, it would not be possible to provide a construction which would be capable of performing a planar motion at an error of less than 1.mu.m by virtue of the presence of the above-noted lifting error.
Still another disadvantage of the proposed conventional table resides in the fact that the corresponding bearing portions are in metal contact so that considerable wear arises whereby, in a short period of time, the precision of the planar motion of the table is adversely affected.